This invention relates to fuel supply control for internal combustion engines equipped with exhaust gas recirculation control systems, and more particularly to a method and a system for control of the fuel sypply to such engines, which is adapted to supply fuel to the engine in a quantity appropriate to an actual quantity of recirculating exhaust gases, to thereby improve the emission characteristics, driveability, fuel consumption, etc. of the engine.
A fuel supply control system adapted for use with an internal combustion engine, particularly a gasoline engine has been proposed e.g. by U.S. Pat. No. 3,483,851, which is adapted to determine the fuel injection period of a fuel injection device for control of the fuel injection quantity, i.e. the air/fuel ratio of an air/fuel mixture being supplied to the engine, by first determining a basic value of the above valve opening period as a function of engine rpm and intake pipe absolute pressure and then adding to and/or multiplying same by constants and/or coefficients being functions of engine rpm, intake pipe absolute pressure, engine temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), etc., by electronic computing means.
It is also known to return part of exhaust gases emitted from the engine from the exhaust passage to the intake passage through an exhaust gas recirculating passage during operation of the engine so as to refrain an excessive rise in the combustion temperature of the air/fuel mixture within the engine cylinders, to thereby prevent generation of nitrogen oxides forming a factor of air pollution, as generally abbreviated as "EGR".
While this exhaust gas recirculation is an effective anti-pollution measure, it has disadvantages as follows: If exhaust gas recirculation is carried out when the temperature of the engine is low, the combustion within the engine cylinders can become unstable, resulting in a degradation in the driveability of the engine. Therefore, at a low engine temperature, the exhaust gas recirculation should be prohibited. Further, during high speed operation of the engine, the rate of recirculation of exhaust gases has to be reduced so as to secure a required engine output and high fuel economy, as well as to maintain desired emission characteristics of the engine. By these reasons, the rate of recirculation of exhaust gases should be varied in response to varying operating condition of the engine so as to always obtain desired amounts of recirculating exhaust gases best suited for various operating conditions of the engine.
If the rate of recirculation of exhaust gases is thus varied, the substantial intake air quantity, that is, the amount of oxygen that effectively contributes to combustion within the engine cylinders varies in response to changes in the rate of recirculation of exhaust gases, even if the absolute pressure in the intake pipe, that is, the intake air quantity into the engine cylinders remains unchanged. Therefore, the quantity of fuel being supplied to the engine should be controlled to appropriate values in response to actual values of rate of recirculation of exhaust gases.